High strength aluminum tubes including tempered 7xxx series alloys have very low room temperature formability. Most frequent tempers for high strength aluminum alloy tubes have the following designations: “F” As fabricated; “H” Strain hardened; “O” Full soft (annealed); “T” Heat treated (e.g., T6); and “W” solution heat treated. Aluminum alloys of the 7xxx series do not have a stable T4 temper and age harden shortly after solution heat treatment and quenching.
Applicants' assignee previously filed published application WO 2015/167588 A1 that discloses a method of forming vehicle rails from extruded 6xxx series aluminum tubes. However, the method disclosed is not amenable to 7xxx series aluminum tubes. 6xxx series aluminum alloys cannot obtain yield strengths approaching 500 MPa. Greater yield strength makes it possible to reduce weight while maintaining desired strength in tubular vehicle body structure reinforcements.
This disclosure is directed to solving the above problems and other problems as summarized below.